package com.jkdl.springboot.common.util.WxUtil;

import org.bouncycastle.jce.provider.BouncyCastleProvider;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.AlgorithmParameters;
import java.security.Security;
import java.util.Arrays;
import java.util.Base64;

public class WxunionidUtil {
    public static String decrypt2(String encryptedData, String sessionKey, String iv, String encodingFormat)
            throws Exception {
        // 被加密的数据

        Base64.Decoder decoder = Base64.getDecoder();
        byte[] dataByte = decoder.decode(encryptedData);
        // 加密秘钥
        byte[] keyByte = decoder.decode(sessionKey);
        // 偏移量
        byte[] ivByte = decoder.decode(iv);
        String result=null;
        try {
            // 如果密钥不足16位，那么就补足. 这个if 中的内容很重要



            int base = 16;
            if (keyByte.length % base != 0) {
                int groups = keyByte.length / base + (keyByte.length % base != 0 ? 1 : 0);
                byte[] temp = new byte[groups * base];
                Arrays.fill(temp, (byte) 0);
                System.arraycopy(keyByte, 0, temp, 0, keyByte.length);
                keyByte = temp;
            }
            // 初始化
            Security.addProvider(new BouncyCastleProvider());
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
            SecretKeySpec spec = new SecretKeySpec(keyByte, "AES");
            AlgorithmParameters parameters = AlgorithmParameters.getInstance("AES");
            parameters.init(new IvParameterSpec(ivByte));
            cipher.init(Cipher.DECRYPT_MODE, spec, parameters);// 初始化
            byte[] resultByte = cipher.doFinal(dataByte);
            if (null != resultByte && resultByte.length > 0) {
                 result = new String(resultByte, encodingFormat);
                //System.out.print(result);
            }

        }finally {
            return result;
        }

    }

}
